Dynamical phasing of Type II Cepheids
In this paper we examine the problems of phasing using light curves andoffer an alternate technique using the changes in acceleration toestablish the zero point. We give astrophysical justification as to whythis technique is useful and apply the technique to a selection of TypeII Cepheids. We then examine some limitations of the technique whichqualify its use.
|
Photometry of Type II Cepheids. II. The Short-Period Stars
We present 668 new photometric observations for 24 Cepheids with periodsless than 3 days. Most of the stars are probable type II Cepheids, butwe have included some type I Cepheids for comparison. A discussion ofthe Fourier parameters of the light curves leads to the conclusion thatthey can be used to distinguish among the several types of light curvesfound among the type II stars but are of limited usefulness fordistinguishing between type I and type II Cepheids. The pulsationalstability is investigated by searching for long-term changes in thelight-curve shapes, period changes, and light-curve scatter. In terms ofthese parameters, the pulsation is more stable than those that werefound for the long-period stars, but for each there are several starsthat show unusually large effects. However, there does not seem to beany obvious difference in light-curve stability of type II Cepheidscompared with type I Cepheids.
|
The Spectra of Type II Cepheids. I. The Hα Line in Short-Period Stars
We present 88 Hα profiles for 24 pulsating variable stars withperiods between 1 and 3 days in order to explore the behavior of thisline in type II as compared with classical Cepheids. Surprisingly, largevelocity differences were found between Hα and the metal lines insome type II Cepheids. Strong emission was observed in three stars, VZAql, NW Lyr, and V439 Oph, while line filling by incipient emission ispresent in seven others. All of the stars with emission and most withincipient emission belong to Diethelm's AHB2 class, and the emission isassociated with the secondary bump on the rising branch of the lightcurve. Two stars, BF Ser and MQ Aql, show doubling of the core nearmaximum light, and asymmetry of the line is noted in some spectra.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
|
Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|
Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
|
Fourier Analysis of Hipparcos Photometry of Cepheid Variables
Fourier parameters have been computed for 240 field Cepheids observed bythe Hipparcos satellite. We have identified three new PopulationIovertone Cepheids: V411Lac, V898 Cen and V572 Aql. We have comparedFourier progressions of Population I and Population II Cepheids. Thepossibility of using Fourier parameters to distinguish between the twotypes is discussed.
|
The intermediate-band approach to the surface-brightness method for Cepheid radii and distance determination
The surface-brightness parameter Fν is calibrated in termsof the Strömgren intermediate-band colour b-y. The relationFν-(b-y)o valid for Cepheids is calibratedusing accurate near-infrared radii and distances for selected Cepheids.We have obtained uvby photometry for non-Cepheid giant and supergiantstars with known angular diameters and compared the slope and zero-pointof their Fν-(b-y)o relation with the Cepheidcalibration. We found that the two calibrations are significantlydifferent. The theoretical models lie in between the two calibrations.It is remarked that Fν-colour relations derived fromnon-Cepheids and involving blue colours (e.g. B-V or b-y) are notapplicable to Cepheids, while those involving redder colours (e.g. V-R,V-K or V-J) also produce good radii for Cepheids. Selected Cepheids ascalibrators lead to the accurate relationFν=3.898(+/-0.003)-0.378(+/-0.006)(b-y)o, whichallowed the calculation of radii and distances for a sample of 59Galactic Cepheids. The uncertainties in the zero-point and slope of theabove relation are similar to those obtained from near-infrared colours,and determine the accuracies in radii and distance calculations. Whileinfrared light and colour curves for Cepheids may be superior inprecision, the intermediate-band b-y colour allows the recovery of meanradii with an accuracy comparable to those obtained from the infraredsolutions. The derived distances are consistent within the uncertaintieswith those predicted by a widely accepted period-luminosityrelationship. Likewise, the resulting period-radius relation from theintermediate-band approach is in better agreement with infrared versionsthan with optical versions of this law. It is highlighted that theintermediate-band calibration of the surface-brightness method in thiswork is of comparable accuracy to the near-infrared calibrations. Thepresent results stress the virtues of uvby in determining the physicalparameters of supergiant stars of intermediate temperature.
|
Period Changes in Population II Cepheids: TX Del and W Vir
We have used the Hipparcos database of epoch photometry to study thevariability of two Population II Cepheids: TX Del and W Vir. We haveconstructed (O-c) diagrams for these stars, using the new data and datafrom the literature. The period of TX Del is decreasing, at a ratewhich is consistent with evolutionary predictions. THe periodchange ofW Vir is uncertain because of the many recent gaps in the data of thisstar. We urge AAVSO visual and photoelectric observers to monitorPopulation II Cepheids more systematically, since amny of these starshave unstable periods, and at least one has an unstable amplitude.
|
UVBY beta Photometric Data and Fourier Coefficients for Galactic Population I and Population II Cepheids
Photometric data in the uvby beta system are presented for a sample of98 Population I Cepheids and seven W Virginis or Population II Cepheids.The importance of the Fourier decomposition technique in the study ofthe structure of pulsating stars is stressed. Mean values and Fourierdecomposition coefficients for the V, b - y, m1, and c1 variations arecalculated. Also, mean values of H beta are provided. New times ofmaximum V light are reported for the majority of the stars in thesample. Significant shifts of the light and color curves were found insome Cepheids; these are explained by their period variations. Thesestars are highlighted in the text.
|
Spectroscopic survey of field Type II Cepheids
A sample of relatively bright, short- and intermediate-period (P=1-10d)Type II Cepheids in the Galactic field have been observedspectroscopically with an intermediate-resolution(lambda/Deltalambda=11000) spectrograph. The wavelength region was6500-6700A, including the Hα line and some photospheric ironlines. The signal-to-noise ratio (S/N) was usually between 50 and 100,depending on weather conditions and the brightness of target stars.Radial velocities were determined by cross-correlating the Cepheidspectra with those of selected IAU velocity standard stars having F-Gspectral types. The internal error of the velocity determination processwas calculated to be about 1 km s^-1. Hα emission and strong linesplitting were observed in BL Her during the expansion phase, but nosimilar phenomenon was detected in any other stars in this programme,except for AU Peg which has an unusual Hα line showing a PCygni-like profile. The velocity curve agrees well with recent CORAVELmeasurements. The velocity gradients in Cepheid atmospheres are studiedusing the Hα minus metallic velocities. Similar data are collectedfrom the literature. It seems that having large velocity differences(v_Hα-v_metal>40 km s^-1) is a characteristic feature of thevery short-period (P<1.5d) and longer period (P>10d) Cepheids.Between these period regions the Cepheid atmospheres exhibit smallervelocity differences. Most of the Type II Cepheids observed in thepresent study fall into this latter category. There might be a tendencyfor classical Cepheids of intermediate period to have larger maximumvelocity differences.
|
A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer.
Not Available
|
BVRIJHK Photometry of Cepheid Variables
Contemporaneous BVRI and JHK photometry are presented for twenty-twoCepheid variables. Nineteen of these variables also have uvby photometryavailable, making them excellent candidates for application of theInfrared Flux Method of distance determination. We are in the process ofacquiring high precision radial velocities of sixteen of these variablesin anticipation of conducting that analysi. (SECTION: Stars)
|
Baade-Wesselink Radius Determination of Type II Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.1833B&db_key=AST
|
Radii and Distances of Cepheids. I. Method and Measurement Errors
We develop a formulation of the Baade-Wesselink method which uses theFourier coefficients of the observables. We derive an explicit, analyticexpression to determine the mean radius from each Fourier order. Thesimplicity of this method allows us to derive the uncertainty in themean radius due to measurement errors. Using simulations and a recentdata set we demonstrate that the precision of the radius measurementwith optical magnitudes is in most cases limited by the accuracy of themeasurement of the phase difference between the light and the colorindex curve. In this case it is advantageous to determine the inverseradius, because it has normal errors.
|
Fundamental parameters of Cepheids. IV. Radii and luminosities.
A temperature scale for Cepheids is presented, based on Genevaphotometry. It uses new atmosphere models computed at various values ofmicroturbulent velocity. The scale so-obtained is compared to other onesand the importance of microturbulence effects is shown. This calibrationis applied to 20 Cepheids for which the variation of microturbulence isknown. The detailed variations of temperature and gravity are derived.The behavior of the photometric gravity is in very good agreement withthe effective gravity (sum of GM/R^2^ and of the derivative of theradial velocity). Thus static atmosphere models can be used to describethe temperature and gravity variations in Cepheids under the followingconditions: i) the microturbulence has to be taken into account, ii) theeffective gravity must be considered instead of the static gravity, iii)in some cases, a small phase interval around minimum radius does notgive reliable results. The temperature and bolometric corrections arethen used to derive radii and distances via the Baade-Wesselinktechnique. The resulting Period-Radius and Period-Luminosity relationsare discussed. Our results compare very well with similar analysis basedon infra-red (JHK) photometry.
|
Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
|
Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
|
Fundamental parameters of Cepheids. III. Turbulence variations.
Observations of the line broadening during the cycle of pulsation areanalysed for 41 Cepheids. The main components of this line broadeningare the stellar atmospheric turbulence and the velocity fields due topulsation and to axial rotation. The variation of the broadening due topulsation is calculated for each star by using the observed radialvelocity curve. The residual broadening at maximum radius allows to showthat the value of the equatorial rotational velocity is smaller than ~10km/s for the large majority of classical Cepheids. It will be shown thatturbulence is the major effect that can explain the variation of thelines widths during the cycle of pulsation. We show that the behavioursof classical and s-Cepheids are different with respect to turbulence anda new method is proposed to separate these classes. This leads to thediscovery of a few new s-Cepheids. The second overtone Cepheid V473 Lyrdoes not follow the sequence of s-Cepheids, that are highly suspected tobe overtone pulsators. It is also shown that the turbulence is in phasewith the acceleration and, particularly, that the maximum turbulence isattained near minimum radius, where the acceleration is also at itsmaximum.
|
A catalog of Cepheid radial velocities measured in 1992-1995 with a correlation spectrometer.
Not Available
|
Mean radial velocities and binarity of Cepheids from 1987-1995 measurements.
Not Available
|
Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
|
Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
|
Fundamental parameters of Cepheids. II. Radial velocity data.
Radial velocity data for 40 Cepheid stars obtained with the CORAVELspectrometer are presented. They represent 1203 individual observations.The mean number of measurements per star is 41, ranging from 10 to 133.For each star, a Fourier analysis has been made and we searched theperiod that gave the best fit for the velocity curve. When the datacovered a sufficiently long time interval, it has been looked for periodchanges or phase jumps. The results have been compared to those found inthe literature; the choice of the best periods is discussed, taking intoconsideration the uncertainty on the period, the smoothness of the fitand several other parameters. New orbital elements, based on CORAVELmeasurements only, are given for DL Cas and W Sgr.
|
Fundamental parameters of Cepheids. I. Photometric data in the Geneva system.
Photometric data in the Geneva system for 26 Cepheid stars are given,representing 869 individual measurements. After a short explanation onthe analysis, the choice of the period and the quality of the fit of thelight curve are discussed. The data and the fitted light- and colourcurves are given, as well as the Fourier coefficients of the best fitfor each star.
|
Summary of Delta S metallicity measurements for bright RR Lyrae variables observed at Lick Observatory and KPNO between 1972 and 1987
From 1972 to 1987 we conducted a survey of the metallicity of faint RRLyrae variables in the Galactic halo, using the 'Butler system' of DeltaS. As part of the calibration of this program, we made approximately 500observations of bright RR Lyraes as abundance standards. We summarizeall the observations of these bright field RR Lyraes and provideaveraged values for the metallicity parameter Delta S. These averagesrepresent the most precise definition of the Butler system for themeasurement of RR Lyrae metallicities. The typical mean error is 0.3units in Delta S, which corresponds to 0.05 dex in (Fe/H). We alsobriefly discuss the weaknesses in the determination of (Fe/H) from DeltaS.
|
New radial velocities for classical cepheids. Local galactic rotation revisited
New centre-of-mass radial velocities are calculated for 107 classicalcepheids from CORAVEL observations. We generally determine thesevelocities from four to six measurements carefully spaced in phase, byfitting a "typical" radial velocity curve or the mirror image of thelight curve. A decomposition in Fourier series is used for stars withmore than 10 measurements. Distances are then computed through aperiod-luminosity-colour relation for 278 classical cepheids with knownradial velocity, and an axisymmetric galactic rotation model is appliedto the sample, using a generalised non-linear least square method withuncertainties on both the velocities and the distances. The bestresults, with a rotation curve modelled as a third order polynomial,are: Rsun_=8.09 +/-0.30 kpc, A=15.92 +/-0.34 km/s/kpc, 2ARsun_=257 +/-7 km/s, A2=d^2theta(R)/d R^2^=-3.38+/-0.38 km/s/kpc^2^, A3=d^3theta(R)/d R^3^=1.99 +/-0.62km/s/kpc^3^, u_0_=9.32 +/-0.80 km/s, v_0_=11.18 +/-0.65 km/s. The effectof modifying the distance scale of cepheids, the absorption coefficientor the fitting procedure algorithm are examined. It appears that theproduct 2 A Rsun_ is very robust towards these changes. Theextended sample of classical cepheids with known radial velocitypresented in this paper seems to imply a higher value for A thananterior studies. The radial velocity residuals show a systematic k-termof about 2 km/s. New evidence from cluster cepheids excludes anintrinsic cause for this shift, and a dynamical cause is proposed from acomparison with a N-body simulation of the Galaxy. The simulation showsthat a systematic bias of this magnitude is typical. The structure ofthe local residual velocity field is examined in some detail.
|
Period-Radius and Period Luminosity Relations for the Classicla Cepheids. I.
The radii of 43 cepheids are computed by the method proposed by theauthor. A relation between the period and the radius for classicalcepheids is derived: log R = (11.9686 +/- 0.0216) + (0.7728 +/-0.197)*log P, where radius is in cm and period is in days.
|
Pulsational study of BL Herculis models. II - Light curves
A survey of the nonlinear pulsational properties of nine sequences oflow-luminosity Population II Cepheids has been made. The resulting lightcurves are discussed and confronted with the observational data. Despitethe fact that the 2:1 resonance with the second overtone dominates thedynamical behavior of the models, the Fourier phase Phi(21) exhibits amonotone, nearly featureless progression as the period ratio P2/P0 isvaried. This progression is very different from the one displayed by theradial velocity curves. It is also dramatically different from thePhi(21) progression found in the classical Cepheid models. On the otherhand, it is in a qualitative agreement with the observed behavior of theBL Her stars. Also, in contrast to the classical Cepheids, we find theremaining Fourier parameters of the models to be extremely sensitive tostellar mass and luminosity. It is shown that a small, observationallyacceptable dispersion of M and L can account for a very large variety ofshapes among the BL Her light curves.
|
Catalog of radial velocities for northern Cepheids measured with a correlation spectrometer
A catalog containing 1446 individual radial velocity values for 79 fieldCepheids and three Cepheids in globular clusters, and 32 averaged radialvelocities of the Cepheid Alpha UMi derived from 100 individual velocityparameters is presented. A table of gamma velocities for 30 Cepheidswith sufficiently good coverage of Vr curves is included. Radialvelocity observations of CE Cas A and CF Cas, which are photometricmembers of the open cluster NGC 7790, made it possible to estimate theradial velocity of the cluster (-78.0 km/s).
|
Pulsational study of BL Herculis models. I - Radial velocities
The linear and nonlinear pulsational behavior of nine sequences of BLHerculis models is studied, and their radial velocity curves arediscussed in detail. The pulsations of these stars, in analogy to theclassical Cepheids, are strongly affected by internal resonances, mostimportantly the 2:1 resonance with the second overtone. This lattercoupling causes a characteristic systematic progression of the Fourierphases and amplitude ratios as the period ratio P2/P0 is varied. Incontrast to Cepheids, the strength of the resonance depends verysensitively on the stellar mass and luminosity, and the morphology ofthe Fourier progression changes significantly when M or L are varied. Inmost of the model sequences, narrow windows are found in which thepulsations exhibit periodic alternations of deep and shallow minima inthe radial velocity and light curves. This behavior occurs for periodssomewhere in the range from 2.0 to 2.6 d, depending on the sequence. Itis caused by the 3:2 resonance between the fundamental mode and thefirst overtone. In the two most nonadiabatic sequences the sameresonance causes windows of chaotic oscillations.
|
INHABITED SKY
